Are Legionella present in sea water?

Legionella bacteria are primarily a freshwater bacteria so can they be found in sea water?

Well, according to research the answer can depend on the level of salinity and the temperature of the water.

More than one scientific study has found that Legionella bacteria can indeed live in sea water but how the bacteria is affected by the sea water depends on the level of salinity and the temperature of the sea water.

A study in 1997 by R Heller et al concluded that salt concentrations up to 1.2% had no toxic effects, that is the equivalent to the salinity in the Baltic Sea for example. At 20oC Legionella bacteria were able to survive salt concentrations of up to 3%. This would be the equivalent of the salinity in the North Sea. However the combination of high temperatures (for example 30-37oC) with salt concentrations over 1.2% decreased the number of Legionella cells.

The report was not able to show whether this combination of salinity and temperature led to the death of Legionella bacteria or the change from culturable Legionella bacteria to viable but non-culturable (VBNC) bacteria.

The possible reasons for Legionella surviving the salinity were put down to the presence of other sea water salts, organic and inorganic components from other bacteria and protozoa. Further the Legionella bacteria may have been adhering to tiny particles in the sea water.

These results were also seen in a 1987 study in Puert Rico where Legionella bacteria were found to be present in marine sites.

It appears then that Legionella bacteria are able to survive in the marine environment, or at least some of them. It is also appears that very few cases of Legionnaires’ disease, if any, have been linked back to infection from sea water but it remains an interesting possibility that sea water is a reservoir for Legionella bacteria.

If you want to discuss the effect of water parameters in your system and how to manage Legionella then contact us via email on

Collaton Consultancy Limited are a specialist consultancy offering technical advice on Legionella, Pseudomonas and water treatment. We also act as Authorising Engineer (Water) in healthcare sites and as Expert Witnesses. We also offer both online and face to face training in a host of subjects.

More information can be found on the following websites:

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.